I did something really stupid
I didn't have much time to shoot my muzzleloader last year, so most of the time it sat in the cabinet. In early November I decided to shoot it at the range to see if the sights were still on as I was dreaming of a distantly possible muzzleloader hunt this last year.
When I got to the range, I saw that they had everything closed off except the 100 yard range, I figured, I'd make do as the rifle was sighted for 100 yards last time I shot it. I posted a target came back to the line and loaded a ball.
After about 5 tries, I could not get it to go off- just a flash in the pan. I tried more priming powder and even tipped the rifle after priming to get some in the flashhole. Still nothing. I poured a little 4f in the flash hole and tried again. This time it went off with a huge boom. A guy down the line said it sounded like a cannon. I shrugged as It had been a year since I shot it last and couldn't remember how loud it was supposed to be. Ichecked my spotting scope and there wasn't a hole in the target.
I loaded another patched ball. Again, I ended up feeding powder into the flashhole to get it to go off. Again, no hole in the target.
When I went to swab the barrel to load another ball, I noticed to my suprise I noticed a badly deformed ball sticking 1/2 way out of the muzzle with no patch under it!
Apparantly there must have been a loose ball in my gun case or something that somehow got into the barrel before I loaded it the first time. The ball must have sealed patent breach so the powder couldn't get in and it took a bit of pressure from priming powder to push it forward enough to ignite the charge.
I shot the rifle aagain, and and it still didn't hit the paper, then fired again at a rock on a berm to find out where it was hitting, but couldn't see where it hit, so I called it a day with the ML. When I got home, I mic'd the barrel and couldn't find any evidence of a walnut, so that was a relief at least.
The mistake I made was that I didn't check the barrel before loading- I could have run a patch puller down the barrel and found the ball, but I didn't.